1. Field of the Invention
The present invention relates to apparatus for steering the beam of a two-dimensional array by a fraction of a beam width in the plane of one of the dimensions of the array. More particularly, it relates to such apparatus in which such steering is effective by actuation of a single selectively variable device. Further the invention relates to such apparatus which is amenable to applications utilizing monopulse feed in the other dimension of the array.
2. Description of the Prior Art
There is a high degree of interest in two-dimensional antenna arrays for airport approach pulsed r.f. beacons. These beacons provide directional beams which have sharp beam pattern skirts at the horizon, and are electronically steerable in the column-plane as the antenna rotates in azimuth to "hopover" rises in ground contour or local structures present at certain azimuthal bearings.
Moreover, this interest is in connection with such two-dimensional arrays which are used with azimuth monopulse feed, and which are consequently designed with separate interconnection of each of their columns to a sum channel and a difference channel. Prior to the present invention electronic column-plane steering for "hopover" required a selectively variable phase shifter for every one of the approximately 500 radiating elements of the array.
Accordingly, there has been a continuing effort to develop apparatus which provides hopover steering in the column plane of a rectangular array with fewer selectively controllable elements needed to effect the steering.